Normally the antibiotic is administered at the end of the mechanical treatment, covering sometimes more - sometimes less - of the treatment period. Bearing in mind the biofilms' ability to resist antibiotics, it is clear that in dental biofilms, the bacteria are not easily/not at all affected by treatment where antibiotics are involved. This possibly explains why SRP and adjunct antibiotic treatment - according to the literature - does not give a better result than SRP alone.